The Tkinter package from Python 2 has been renamed to tkinter in Python 3, as well as other modules related to it.
Here is a list of renamed modules:
Tkinter→tkintertkMessageBox→tkinter.messageboxtkColorChooser→tkinter.colorchoosertkFileDialog→tkinter.filedialogtkCommonDialog→tkinter.commondialogtkSimpleDialog→tkinter.simpledialogtkFont→tkinter.fontTkdnd→tkinter.dndScrolledText→tkinter.scrolledtextTix→tkinter.tixttk→tkinter.ttk
I advise you to learn how to dynamically browse the modules with the dir command. If you are under windows, configure Python to use readline module to get auto-completion and make it much easier to list available classes in a module.
For a description of each module, refer to the official Python documentation. (Tkinter in Python 2.x, tkinter in Python 3.x)